In the care of infants, and particularly premature infants, it is frequently necessary to substantially continuously monitor their heart functions and many premature infants also require frequent X-rays of the upper chest area to evaluate lung conditions. However, premature infants usually have a very low birth weight and require very little radiation to generate an X-ray so that metal parts and even some non-metalic parts having significant mass which are located in the infant's chest area during the X-ray, will produce images on the X-ray film. Thus, if the electrodes or the lead wires or any connections between the electrode and the lead wires disposed within the chest area of the infant have metallic parts or even non-metallic parts of substantial mass, they should be removed each time an X-ray is taken and then replaced. Removing and replacing the electrodes is not only time consuming but also increases the likelihood of dermal irritation or ulceration to the very thin skin of an infant. Further, monitoring is interrupted whenever the electrodes are removed.
The patent literature discloses various electrode constructions described as being X-ray translucent. Some such as described in U.S. Pat. No. 4,257,424 use a thin layer of conductive paint on a thin flat elongated substrate to form both the electrode and an extended lead, and others such as disclosed in U.S. Pat. Nos. 3,888,240 and 4,748,983 form a sheet electrode and a lead strip from a conductive carbon filled plastic material. The leads in such electrode assemblies are in the form of thin and relatively wide uninsulated bands and present some problems in handling and insulating, particularly if the leads are made sufficiently long to extend outside of the patient's chest area. Some other electrode constructions such as disclosed in U.S. Pat. No. 4,685,467, use a button type electrode with a snap-on connector to connect the lead wire to the electrode. The button electrode with snap-on connector has a substantial mass which not only reduces the X-ray transparency of the electrode assembly, but also produces an uneven and relatively high profile electrode assembly which would be uncomfortable if positioned on the back of a patient. Electrodes have also been heretofore made in which sheathed carbon fiber conductor was connected to a carbon filled disk type electrode by sonic welding. However, sonic welding can only be used with relatively thick disk electrodes which are not X-ray transparent.
It is an object of the present invention to provide a biomedical monitoring electrode adapted to be adhesively affixed to the patient for continuous ECG monitoring, and in which the overall electrode assembly including the electrode member and electrical lead means and the connection between the electrode and the electrical lead means are X-ray transparent even at the relatively low level exposures used in infant X-rays, so that it is unnecessary to remove and replace electrodes in the chest area when taking X-rays.
A more particular object of this invention is to provide a biomedical monitoring electrode assembly including a multi-element back electrode adapted to be adhesively affixed to the back of an infant, and a reference electrode adapted for positioning remote from the back electrode and in which the back electrode including the leads and the connection between the electrodes and leads is X-ray transparent so that it is unnecessary to remove and replace the electrodes when taking chest X-rays.